In semiconductor device manufacturing, plasma etching using a processing gas may be carried out in fine processing of a thin film formed on a workpiece. The thin film may, for example, be a silicon compound film such as a silicon nitride film or a silicon oxide film, or may be an organic film having carbon as a main component that is formed from amorphous carbon, a photoresist composition, or the like. Of these examples, in a case in which a silicon oxide film is an etching processing target, it is necessary to selectively etch the processing target silicon oxide film relative to a non-processing target film formed on the same workpiece, such as a silicon nitride film or an organic film. In other words, it is necessary to increase the selectivity in etching.
For this reason, various processing gases for plasma etching have previously been proposed with the aim of sufficiently increasing selectively in etching, and enabling sufficiently selective and efficient etching of a processing target (for example, refer to PTL 1). PTL 1 describes a plasma etching method in which a fluorocarbon such as C4F6, C4F8, or C5F8, or a hydrofluorocarbon such as CH3F or C5HF7 is used as a processing gas in etching of a silicon oxide film.
Moreover, demand for weight-reduction, miniaturization, and densification of semiconductor devices has been increasing in recent years. In association with this demand, it is becoming important not only to improve selectivity in etching, but also to improve the accuracy of processed shape obtained through etching when a fine structure such as a self-aligned contact hole is formed by etching on a workpiece including a silicon compound film or an organic film. In general, a protective film is formed on a non-processing target in order to prevent etching of the non-processing target in plasma etching. However, particularly in the case of self-aligned contact hole processing, it is difficult to form a protective film on shoulders of a spacer formed by a silicon nitride film. Consequently, when a processing target silicon oxide film adjacent to the silicon nitride film forming the spacer is etched, shoulders of the silicon nitride film forming the spacer are also susceptible to etching. In some cases, this results in thinning or loss of shoulders of the spacer by a stage at which the etching process ends (for example, refer to PTL 2 and PTL 3). In the present specification, the loss of shoulders (corners) of a structure such as a spacer formed by a non-processing target is also referred to hereinafter as “faceting”. In general, a spacer is used to insulate a gate material and metal wire that may be formed by embedding a metal wire material in a contact hole. Accordingly, thinning or loss of the spacer may cause a short-circuit between the gate material and the metal wire, leading to loss of function as a semiconductor device. Therefore, faceting has become a significant issue in semiconductor device manufacturing.